1. Field of the Invention
This invention relates to a speaker system to be installed in the passenger compartment of a vehicle and more particularly to the installation of a speaker unit in the door, beneath the rear tray or in the dashboard of a vehicle such as an automobile.
2. Background Art
FIG. 1 shows a speaker unit 1 of a conventional speaker system installed in a door 2 of a passenger-carrying vehicle. FIG. 2 shows another speaker system wherein the speaker unit 1 is enclosed with a waterproof cover 4 beneath a side-window glass 3. FIG. 3 shows still another speaker unit 1 of a speaker system installed in a trunk 7 beneath a rear tray 5 and behind a rear seat 8. The speaker unit faces a rear window glass 6. A description will subsequently be given of the installation of a speaker system in the above cases.
The speaker unit 1 of the conventional speaker systems has its rear surface opened into the door 2 or the trunk 7 or possibly the waterproof cover 4 forming an airtight chamber.
Even though the speaker unit 1 of the conventional vehicular speaker system has a flat frequency response, the sound pressure level has peaks respectively in the neighborhoods of 250 Hz and 1 kHz as shown in FIG. 4 from the effect of standing and reflected waves inside the vehicle. Furthermore, there is a dip in the neighborhood of 600 Hz. Thus the installed speaker system exhibits steeply peaking and dipping characteristics.
Furthermore, a dip appears in the vicinity of 800 Hz and a peak appears in the vicinity of 1 kHz if the speaker unit 1 is provided with the waterproof cover 4 as shown in FIG. 2. When the frequency response of the speaker unit 1 is combined with those inside the vehicle, the sound pressure level will show characteristics that are further steeply peaked and dipped.